1. Field of the Invention
The present invention relates to a process for the preparation of a methacrylimide group-containing polymer having excellent optical characteristics, especially a light-transmitting property, and a light-transmitting fiber having a core-sheath structure comprising a methacrylamide group-containing polymer obtained by this process as the core component.
2. Description of the Related Art
Recently, transparent resins have been used in large quantities for high-performance optical materials, decorative materials, automobile parts, electric appliances and the like. These transparent resins are often used at high temperatures, and currently there is a strong demand that transparent resins should have not only a high transparency but also a high heat resistance. Namely, transparent resins in which excellent optical characteristics can be maintained for a long time, even at a high temperature, are required.
An imide group-containing polymer is known as a transparent resin having a heat resistance, and as the process for preparing this imide group-containing polymer, there have been proposed, for example, (1) a process in which a polymer of acrylic acid, methacrylic acid or an ester thereof is heated and reacted with a primary amine, ammonia or a primary amine-generating compound (U.S. Pat. No. 2,146,209), (2) a process in which a polymer of methyl methacrylate is reacted with a primary amine in the presence of water (U.S. Pat. No. 3,284,425), and (3) a process in which an acrylic polymer is reacted with ammonia or a primary amine in an extruder (U.S. Pat. No. 4,246,374).
The imidized polymers obtained by these processes have improved heat resistance, but these polymers have problems in that the optical characteristics thereof, especially the resistance to coloration under heating, are poor.